1. Field of the Invention:
This invention relates to rigid or hard disk drives that store information, or data, on rotating magnetic disks. More particularly, this invention relates to control of the flying height of a read/write magnetic head as a rotating magnetic disk spins under the head.
2. Description of Prior Art:
A significant limitation on data density in hard disk drives is the "spacing loss" which is the reduction in signal quality due to distance (fly height) between the read/write head and the magnetic recording surface of the disk. The shorter the fly height is, the higher the potential data density is.
U.S. Pat. No. 4,777,544 of Brown et al, commonly assigned with this application, describes a method and a means for measurement of head/disk spacing by use of a harmonic ratio fly height circuit. The '544 patent is directed essentially to measurement of average fly height along a track, and use of that information during the manufacture of the drive. There is no provision for measuring circumferential variations in fly height around a recording track.
Closed loop control of fly height in a single-disk drive having a rigid support for the read/write head is shown in Japan Pat. 02-263306, and U.S. Pat. No. 4,146,911. In U.S. Pat. No. 4,146,911, the head arm is moved relative to the surface of the disk to change the fly height. In Japan 02-263306, a piezoelectric block between the arm and the read/write head is excited to change the fly height. Neither patent shows a conventional multiple-disk arm assembly consisting of a rigid comb with suspension arm attached to the end of each comb blade, and a floating head-suspension attached to the end of each suspension arm. The fly height control structures in these two patents are not practical for hard disk drives with flexible suspension systems such that the head fly height depends on the flying characteristic of the head as well as the suspension system.